A feeding device integrated in an ink jet printer, with the purpose of picking and feeding the sheets from a tray along a printing path towards an ink jet printhead with which the printer is provided, and having substantially the characteristics specified above, is described in an European patent application previously filed by the Applicant and published with No. EP 0 873 876.
In detail, in this previous device, the tray is arranged according to a substantially vertical orientation, so that the sheets of the ream rest and are aligned, through the effect of their weight, against a back wall of the tray. In particular, the sheets are aligned against this back wall along the respective front edges, by means of which the sheets access the printing path. During the approach motion of the tray to the main feeding roller, the front edges of the sheets travel a predetermined path, along which they come into contact with the auxiliary roller, which in turn, being connected in the rotation to the same members that control the movement of the tray, rotates jointly with the approach motion of the latter.
Accordingly this device has the non-negligible drawback that the sheets of the ream can crumple and bend, or even just become deformed, local to their front edge, by coming into contact and sliding against the auxiliary roller, while it rotates, with the risk of accordingly compromising the regular picking of one sheet at a time from the ream and its correct feeding along the printing path by means of the main feeding roller.
In addition, there is the further drawback that the possible crumplings of the front edge produce interference and slide against the printhead, thus dirtying the sheets and/or at any rate causing visible defects thereon, liable to have a negative influence on the quality of printing obtainable using the printer.
Also, the above-mentioned device uses a monodirectional bushing, also called free wheel, for controlling the line feed motion of the sheets during their printing, its function being to connect in rotation a main feeding gear, in turn made revolve by a main motor, with a main feeding roller in contact engagement with the sheets for feeding them along the printing path, only when the main feeding gear rotates in a predetermined direction, leaving it free to rotate with respect to the main feeding roller, when the main feeding gear rotates in the opposite direction.
This solution has the drawback that when the main feeding gear stops at the end of each elementary rotation defining the pitch of the line feed motion of the sheets, the feeding roller tends by inertia to advance at an angle beyond the feeding gear, even though only to a very small extent, determining an error in the line feed motion pitch. As a result, this error, accumulating with other successive ones, may significantly reduce the quality of printing obtainable on the sheets, especially when the dot printing produced with the ink jet head is of the high definition type, and accordingly requires, for best results, the line feed motion of the sheets to be extremely precise, in order to permit the depositing of the droplets ejected by the ink jet head with absolute exactness on the sheets.